Mold permitting air ejection of a flanged article

ABSTRACT

An article having a flange is molded between a mold core and a unitary mold cavity, the flange being formed during the process as a consequence of the existence of an undercut existing in a first surface of the cavity. A ridge is provided on a second surface of the mold cavity adjacent the undercut. A fluid, i.e., air, is injected between the cavity and the molded article as the core and cavity separate in such a volume and at such a pressure as will maintain the article in substantially complete and constant contact with the core as the core and article are withdrawn from the cavity. The flange conforms to the cavity wall until the article is free from the cavity, and subsequently the molded article is separated from the mold core.

This is a division application of Ser. No. 6,321,570 filed Nov. 16,1981.

The present invention is directed generally to molds and processes ofmolding thermoplastics to form articles having particularly desirablefeatures. The invention is directed particularly to a mold having aunique design, articles formed by injection-molding thermoplastics in amold of that design, and the process of removing such articles from themold so as to retain features created in the molding operation.

The injection-molding of thermoplastics is a well-known process by whichplastics generally in granular pellet or powdered form are first heatedto a viscous melted state and then injected under high pressure into amold where the plastic cools to a solid shape conforming to the contoursof the mold walls. The resulting articles are usually finished partsrequiring no further work prior to assembly into or use as finishedproducts. Many details of the finished parts or finished products suchas bosses, flanges, locating pins, ribs, bushings, mounting holes, andthe like have been molded as a single operation, and the design ofinjection molds for creating such details is an advanced art.

In general, a mold comprises a mold cavity and a mold core, the moldedarticle being formed between the opposed core and cavity when theviscous melted thermoplastic is injected into the space between the coreand cavity. When the article is sufficiently cool so as to retain itsshape, the core and cavity separate one from the other and the articleis then removed, usually with the aid of an ejector means, from thespace between the core and cavity.

In order that many details such as bosses, ribs, mounting holes, and thelike might be formed, the mold may include additional specialized moldcomponents. For example, a hole or small detail in a molded article isoften formed by having a core pin extending into the cavity. Undercuts,flanges, and other similar configurations have been made by having asplit cavity or a side core or slide-action element as part of thecavity. Such slides and side cores are caused to retract the criticaldistance before or during the mold opening, thereby freeing theentrapped section of the article and allowing its ejection. Typically,the retraction or core pulling is actuated in a number of ways, eitherby hydraulic or air cylinders, springs, or mechanical cam action. Thedisadvantage of such split cavities, side cores or slide-action elementsis that the design and execution of the mold with the action elementsare much more exacting and expensive than molds having no movingelements other than merely the core and unitary cavity.

Therefore, an object of the present invention is to design a cavitywhich will form an undercut, flange, or other similar configuration onan article which can be ejected without requiring any side core orslide-action element in the mold.

Another object of the present invention is to employ such a mold incombination with a molding apparatus in a particular manner so as topermit ejection of the molded article from the mold in the absence ofany side core, slide-action, or other moving element to the mold.

A further object of the present invention is to design articles havingincidental features placed adjacent to flanges and the like which willpermit extraction from the mold in the absence of any side core orslide-action element in the cavity of the mold.

A particular object of the present invention is to form a straight wallcontainer having a radially outwardly extending flange at the bottom ofsaid container, which flange may be formed in a unitary mold cavity andextracted from the cavity in the absence of any partition of the moldcavity.

These and other objects of the present invention are achieved byincluding in a unitary mold cavity an undercut or other configurationwhere an article formed in the mold would not normally be able to befreed by the mold opening in the absence of some slide-action element,and incorporating in that mold means for injecting a fluid between thecavity and the formed article in the cavity as the core and cavityseparate in such a volume and at such pressure as will maintain theformed article in substantially complete and constant contact with thecore until the article is free from the cavity. Once the article is freefrom the cavity, the article is then separated from the core in aconventional manner.

The adjective "unitary," when applied to mold cavities in thisapplication, is intended to mean that the cavity has no side core orslide-action element and is not a split cavity which separates one partfrom the other. A unitary mold cavity, as that term is used in thisspecification, may be constructed of more than one piece of metal; butif so constructed, the pieces remain in fixed relation one to the otherthroughout the molding operation.

In particular, the invention is directed to the process for molding anarticle between a mold core and a unitary mold cavity, the articlehaving a flange being formed during the process as a consequence of theexistence of an undercut existing in a first surface of the cavity, byproviding a means on a second surface of the mold cavity adjacent theundercut for forming a flexural region in the article in proximity tothe flange, injecting a fluid between the cavity and the molded articleas the core and cavity separate in such a volume and at such a pressureas will maintain the article in substantially complete and constantcontact with the core as the article is withdrawn from the cavity, theflexural region allowing the flange to conform to the cavity wall untilthe article is free of the cavity, and subsequently separating themolded article from the mold core in a conventional manner.

Further, the invention is directed to molded articles having a flangeformed during the molded process on a first surface of the article andhaving a groove or other means formed on a second surface of the articleadjacent the flange, the groove or other means being of such aconfiguration as will permit the flange to collapse at least partly intothe groove or other means while the article is being removed from themold cavity.

A particularly advantageous feature achieved by the present invention isthe inclusion of a radial flange at the bottom of a straight wallcontainer, the flange extending radially outwardly to permit theretention on the straight wall container of a circumferentiallyencompassing label of paper or the like which is applied to thecontainer subsequent to being molded to identify the contents within thecontainer.

An advantage of the present invention is the formation of flanges andother configurations in articles of molded thermoplastics in the absenceof any split cavity or a side core or slide-action element in the cavityof the mold forming such an article, thereby greatly simplifying molddesign.

These and other features and advantages of the present invention willbecome apparent to those skilled in the art upon considering thefollowing description of preferred embodiments and examples illustrativeof the invention together with the accompanying figures, wherein:

FIG. 1 is a sectional view of a mold incorporating the features of thepresent invention;

FIG. 2 is a sectional view of the mold shown in FIG. 1 with the mold inthe process of ejecting a molded article therefrom;

FIG. 3 is a sectional detail of the mold shown in FIG. 1;

FIG. 4 is a sectional detail of the view shown in FIG. 3 with the moldedarticle in the process of being ejected from the mold;

FIG. 5 is a sectional detail of an alternative embodiment of a moldaccording to the present invention; and

FIG. 6 is a sectional detail of the mold shown in FIG. 5 at the pointthat the article is free from the mold cavity.

FIG. 1 shows a mold 10 comprising a core 12, a unitary cavity 14, and astripper ring 16 for removing the molded article 18 from the core 12.The unitary cavity 14 includes a locating ring 20 and a sprue bushing 22through which the molten viscous plastic is injected into the spacebetween the core 12 and cavity 14 to form the article 18. A valve 24 isincluded in the cavity 14, the valve being biased toward a closedposition such that a surface 26 of the valve is a continuation of thesurrounding surface defining the space between the core 12 and cavity 14in which the molded article 18 is formed. The valve 24 is connected to asource (not shown) of high-pressure fluid such as air through conduit28.

The article 18 shown in FIG. 1 constitutes a container having a straightwall 30 having an outwardly flared lip 32 at the mouth of the container.The bottom 34 of container 30 is generally planar, and includes a flange36 which extends radially outwardly beyond the outermost dimension ofthe straight walls 30. It was the practice of the prior art, whenforming an article such as 18 having an outwardly extending flange 36,to form such an article in a split cavity, the walls of which would moveoutward so as to permit withdrawal of flange 36.

In accordance with the present invention, after the article 18 has beenformed in the space between the core 12 and cavity 14, a fluid such asair is supplied through conduit 28 and valve 24 just before or as themold opens, the fluid thus being applied to the bottom 34 of thecontainer at a pressure and volume such as will maintain the bottom 34in substantially complete and constant contact with core 12 as the core12 and article 18 are withdrawn from cavity 14. The flange 36 deflectsradially inwardly and acts as a sealing ring around the periphery of thebottom 34 of container 18 as the container 18 and core 12 withdraw fromthe cavity 14. As the flange 36 encounters the lip 38 of the cavity, theair or other fluid in the cavity will cause the flange 36 to reassumeits originally molded position. The container 18 can then be removedfrom core 12 by conventional means such as with the aid of the stripperring 16. It will be appreciated that an ejector sleeve, ejector blade,or stripper plate may be used in lieu of the stripper ring 16. After theflange 36 of the container has expanded outwardly after clearing lip 38of the cavity, the air or other fluid being injected through conduit 28can be eliminated and valve 24 will reassume its closed position shownin FIG. 1.

In FIG. 3, a detail taken from FIG. 1, it will be seen that flange 36extends a radial distance R outside the diameter D shown in FIG. 2. Byway of example, a container 18 according to the present invention wasmolded in a mold substantially as illustrated in FIGS. 1-4 wherein theoutside diameter D was 4.25 inches with the thickness of wall 30 beingtypically 0.062 inch. The flange 36 projected a distance R=0.120 inch.There was provided a groove 38 in the bottom 34 of the container 18, thegroove 38 being approximately centered but perhaps slightly inside thecenter of wall 30, the depth of the groove being approximately one-halfthe thickness of bottom 34. The container was molded out of UnionCarbide 7904 at the temperature and pressure suggested by themanufacturer of the resin. Air was introduced against the bottom 34 ofthe container at a pressure of about 100 psi in sufficient volume tomaintain that approximate pressure as the core 12 was withdrawn from thecavity 14. As the flange 36 cleared the lip 38 of the cavity, theintroduction of air into the cavity was terminated and the flange 36returned to the original position illustrated in FIG. 3. The cycle timefor the molding procedure was approximately 8 seconds, with the timebetween completion of injection and mold opening being approximately 1.5seconds. These times were about the minimum times possible under theparticular molding conditions employed. The container thus formed wassatisfactory in every respect, the flange 36 being permanently fixed ina radially outward position as originally molded. It will be appreciatedthat the dimensions and times given are merely intended as an exampleand not by way of limitation on this invention.

As will be seen in FIG. 4, the groove 38 is caused to reduce indimension as flange 36 deflects radially inwardly when the core 12 andcontainer 18 are withdrawn from cavity 14. The radially outward forceexhibited by flange 36 on the inside wall of cavity 14 acts to seal thecavity, thereby permitting large pressures to be built up within thechamber 40 which is created as the core 12 and article 18 are withdrawnfrom cavity 14. It is believed that groove 38 is necessary in order thatthe inward flexing of flange 36 can occur. In the absence of groove 38,the flange 36 is torn from the bottom of the container wall 30 or ispermanently deformed in such a manner as will prevent flange 36 fromreturning to the originally molded position once the container 18 isfully removed from cavity 14.

While the container illustrated in FIGS. 1-4 is a straight wallcontainer, it will be appreciated that both flared and reversed draftcontainers might also be formed having a flange such as that illustratedin the bottom utilizing the unitary cavity intended by this invention.The design of the valve 24 is not critical to the invention, but valve24 must permit the introduction of fluid into chamber 40 which is formedas the core 12 and container 18 are removed from cavity 14 at such apressure and in such a volume as will maintain bottom 34 insubstantially complete and constant contact with the core 12 until thearticle 18 is free from cavity 14.

Another embodiment of an article 42 formed according to the presentinvention is shown in FIGS. 5 and 6, the article 42 having a bottom 44smoothly merging with a first side section 46. At a top of the firstside section 46, an outwardly flared portion 48 extends radially outwardand includes a flange 50. A second wall portion 52 extends upwardly fromradially flared portion 48 inside the dimension of flange 50 and at anupward edge thereof tapers outward over tapered portion 54. A groove 56is provided in the bottom of the radial portion of the article 42adjacent flange 50 in such a manner as to permit the inward flexing offlange 50 at such time as the molded article 42 is removed from cavity58. A valve 60 is provided adjacent the bottom 44 of the article 42through which can be injected a fluid such as air. As the article 42 andcore 62 are withdrawn from the cavity 58 as shown in FIG. 6, the flange50 collapses radially in part into groove 56, and the pressurized fluidentering through valve 60 maintains the bottom 44, first side portion46, and radial portion 48 in contact with core 62. As the core 62arrives at the position shown in FIG. 6, the flange 50 expands outwardto resume the position shown, thereby forming the outwardly extendingflange desired in the finished article 42. The position shown in FIG. 6is deemed to be that position where the article 42 is "free from thecavity" and is the point at which the introduction of fluid throughvalve 60 can be terminated.

The process of the present invention may be employed to produce variousconfigurations, and is not intended to be limited to merely thecontainer art. Nevertheless, the invention has particular utility in themanufacture of containers having a radially outwardly extending flangeon the bottom of the container. It will be appreciated that where aflange is formed on the bottom of a container according to the methoddisclosed, the container will include a groove on a bottom surface ofthe container approximately aligned with the wall of the container forpermitting the flange to collapse radially inwardly during the ejectionphase of the molding process, the flange emerging from the mold andre-orienting itself to its original molded position. As the flangedimension R increases, it is believed that the wall thickness and groovesize must also increase to permit the necessary radially inward collapseof the flange during ejection.

While the invention has been described with reference to a specificexample and various embodiments, it is intended that the embodiments inthe example be illustrative and not limiting, the limits of theinvention to be found solely in the appended claims.

What is claimed is:
 1. A mold for forming an article having a wall and aflange projecting radially outwardly therefrom, comprising a unitarymold member defining with a movable core a cavity for forming saidarticle, an undercut provided in a first surfaces of said mold memberfor forming said flange, a means provided on a second surface of themold member adjacent to the undercut for forming a flexural region inthe article in proximity to the flange, and means in the second surfacefor supplying a fluid between the cavity and the formed article in sucha volume and at sufficient pressure to maintain the article insubstantially constant contact with the core as the core is removed fromthe cavity, the flexural region allowing the flange to conform to thewall of the cavity until the article is free from the cavity.
 2. Themold of claim 1 wherein said means provided on a second surfacecomprises a ridge for forming a groove to permit the inward flexing ofthe flange during removal from the cavity.